1. Technical Field of the Invention
This invention relates to an electric vehicle, and more particularly to an electric vehicle frame and a method of assembling the electric vehicle using the frame and a plurality of subassemblies.
2. Background of the Invention
Electric vehicles are well-known forms of transportation. These vehicles can be classified as automobiles, motorcycles, and motor scooters. Automobiles are four-wheeled vehicles. Motorcycles are two-wheeled vehicles, which are straddled by the rider. Scooters are two or three-wheeled vehicles that have a step-through portion to facilitate mounting and seating of the rider. In the case of three-wheeled scooters, these may be useful as all-terrain vehicles due to the wide base the spaced rear wheels provide. One distinguishing characteristic, which separates motorcycles and scooters, is that scooters include the step-through portion, which is a gap in the vehicle body between the handlebars and the seat that allows riders to easily mount the scooter and sit thereon with their legs together in front of them. Motorcycles, on the other hand, have a continuous vehicle body, which forces the rider to sit with their legs apart straddling the vehicle body.
In an effort to decrease the impact of gas-powered vehicle emissions on the environment, electric motor scooters have been developed. These scooters generally include a tubular frame for supporting the components of the vehicle and a power unit. The power unit typically is a battery pack. These tubular frames are formed by welding steel pipe members into a unitary, skeletal structure. As disclosed in U.S. Pat. No. 5,613,569, a tubular frame supports a battery case underneath. A number of body panels are attached to the frame to completely conceal the frame and side portions of the battery case.
There are a number of drawbacks to this type of configuration. First, this frame is constructed of steel, which in order to provide sufficient structural strength significantly increases the weight of the vehicle. Vehicle weight reduction is critical in electrical vehicle applications, because maximizing the range of the scooter requires minimizing the weight. Therefore, it is desirable to construct the frame in such a manner that significantly reduces the vehicle weight.
Second, tubular frames require significant manual labor in order to join the pipe members together. Such labor intensive assembly methods are costly and undesirable. Third, the tubular frame and battery case disclosed in that patent requires an air exhaust device to move cooling air within the battery case to cool the batteries. This is undesirable since it adds complexity to the configuration and increases the vehicle weight.
U.S. Pat. No. 4,334,589 discloses a frame for a motorcycle. This patent discloses a shell type frame, which includes an upper half shell and lower half shell detachably joined together at the peripheral edges. The upper half shell includes a steering tube for receiving a steering assembly. A conventional gasoline engine is the power unit. The engine is connected to opposite sides of the shell so that the engine is a mechanical strength member. Once assembled, the front and rear of this frame are open to allow air to pass through the frame and cool the power unit. Motorcycles have acceleration and driving performance requirements that are largely different from motor scooters. For this and other reasons, the frame of that patent is not desirable for use in a motor scooter. First, the frame does not provide the necessary step-through portion required by scooter riders. Secondly, the frame does completely enclose the power unit from the environment. This is critical for electric vehicle applications, since exposure of the batteries to moisture can damage the power unit.
Therefore, an improved electric vehicle frame and more advantageous method of assembling an electric vehicle using the frame are sought. It is desirable that the frame be lightweight, yet still provide sufficient structural support for the vehicle. It is furthermore desired that the frame allow rapid yet simple assembly and construction of the vehicle while still protecting the power unit from weather.